In order to increase the output and torque, but also to reduce the fuel consumption and exhaust emissions, of internal combustion engines for road vehicles, cam shaft phase setters for varying the inlet and also outlet control times have become widespread. Due to their high degree of reliability, but also in view of a favorable cost-benefit relationship, hydraulic phase setters which are operated using the lubricating oil for the combustion engine in accordance with the principle of the hydraulic pivoting motor have proven to be of value. Increased demands on fuel consumption and emissions require high setting speeds. A compact, space-saving design and a low price of the phase setter are also demanded. At the same time, faultless operation and a high degree of reliability are to be ensured.
The demands for a high setting speed and a compact design are met by phase setters comprising a central control valve. In order to ensure operational reliability while keeping the dimensions and the losses due to leaks as small as possible, the pressure fluid which serves to adjust the phase setter—in most applications, the lubricating oil for the combustion engine—is cleaned by means of filters upstream of the phase setter and as near to the phase setter as possible. With regard to operational reliability, arranging a blocking member, for example a reflux valve, in the pressure fluid feed of the phase setter and so preventing one or more setting chamber(s) of the phase setter from being able to be emptied in the direction of the upstream pressure fluid supply if a pressure burden prevails in the setting chamber or chambers as compared to a pressure fluid supply which feeds the pressure fluid is also known. Such a pressure burden can occur in a phase setter due to the drag moment of the cam shaft.
In accordance with JP 09-280019, a filter device is arranged immediately upstream of the phase setter in the pressure fluid feed to the phase setter within the cam shaft. A disadvantage of this solution is that mounting space has to be provided on the part of the cam shaft for the filter device, and the filter device has to be inserted into the cam shaft in an assembling step of its own.
DE 10 2005 052 481 A1 discloses a phase setter which comprises a central control valve comprising an integrated filter device and an integrated reflux valve. The control valve comprises a valve housing which is arranged axially in relation to the rotational axis of the cam shaft and which comprises a valve inlet, control ports and a radial valve outlet. A valve piston is accommodated, such that it can be moved axially, in the valve housing. In a first variant, the filter device is arranged in the valve inlet. The pressure fluid flows radially through the valve inlet and the filter device into the interior of the valve housing, where it flows axially onto the reflux valve and past the reflux valve in a radial direction into a channel which extends axially in the valve housing, from which it flows radially inwards to the outer circumference of the valve piston, via the outer circumference of the valve piston to one of the control ports and via the relevant control port to assigned setting chambers of the phase setter. Pressure fluid flowing off from other setting chambers is channeled via the other of the control ports into and through the valve piston to the valve outlet. In a second variant, the filter device is not arranged in the radial valve inlet but rather in an axial portion of the valve housing which is connected to it and upstream of the reflux valve. In both variants, there is either only a small filter cross-section available for cleaning the pressure fluid, or additional mounting space for arranging the filter device is required.
A filter device which cleans the pressure fluid in the radial feed is also known from DE 10 2009 048 753 A1, in which the filter device is formed as a filter ring which is to be assembled separately.
In order to reduce an increased risk of swarf associated with the filter device of DE 10 2005 052 481 A1, DE 10 2008 006 179 A1 proposes constructing the valve housing in three layers. A filter fabric surrounds an outer circumference of an inner guiding sleeve. Plastic is injection-molded around the outside of this two-layered sleeve body. The filter fabric extends axially through radial control ports of the three-layered valve housing. The size of the filter cross-section is also limited in this solution, since only the cross-section of the respective control port through which the pressure fluid flows on its way to the pressure chambers is available as the filter cross-section. The three-layered construction of the valve housing also increases the effort of manufacturing and the price of the control valve.
Phase setters comprising central control valves and reflux valves integrated in the control valves are also known from U.S. Pat. No. 6,971,353 B2 and U.S. Pat. No. 7,533,695 B2. U.S. Pat. No. 7,533,695 B2 mentions that a filter device can optionally also be integrated in the control valve.